A wireless communication network in conformity with a cellular communication system represented by a mobile phone network constitutes a wide service area by distributing dispersively a plurality of base stations (eNB: evolutional Node B). Then, each of these plurality of base stations forms and manages “cell” which is an area where the base station itself and a mobile station (UE: User Equipment) such as a mobile phone can communicate with each other.
Further, a mobile station which communicated with a base station managing a certain cell, due to the mobile station's movement, performs handover which is a process to change a communicating counterparty to another base station managing another cell near this certain cell.
Here, in a general mobile communication system, a mobile station which needs handover receives radio wave respectively transmitted from peripheral base stations on the basis of neighbor cell information (NCL: Neighbor Cell List) which is a list of peripheral base stations. Then, the mobile station detects a base station from which the mobile station can acquire the best reception quality and performs handover to the base station. In this way, the mobile station has only to perform reception quality measurement for cells included in the neighbor cell information, and therefore, it is possible to select a cell efficiently.
Utilization of neighbor cell information in a general technique is explained below using concrete examples.
Referring to FIG. 1, this example includes a mobile station (which is written as “UE” in FIG. 1) 700 and a cell group 800. Further, the cell group 800 includes “Cell #1, Cell #2, Cell #3, Cell #4, Cell #5, Cell #6 and Cell #7”. Meanwhile, respective cells in the figure are generated and managed by a base station 900 whose illustration is omitted in the FIG. 1.
This example is explained by focusing on Cell #1 which is a cell where the mobile station 700 is currently located. Here, neighbor cell information which shows cells being adjacent to Cell #1 includes “Cell #2, Cell #3, Cell #4, Cell #5, Cell #6 and Cell #7”.
Next, referring to FIG. 2, a sequence when the base station 900 notifies the mobile station 700 of the neighbor cell information is explained.
Firstly, the base station 900 which forms and manages Cell #1 transmits notice information to the mobile station 700 (Step S91). The notice information is used for measuring a situation regarding wireless communication of cells near a cell where the mobile station 700 itself is currently located when the mobile station 700 performs connection or reconnection to any cell or handover (HO: Handover) to another cell.
Firstly, in Step S91, the neighbor cell information “Cell #2, Cell #3, Cell #4, Cell #5, Cell #6 and Cell #7” which is information representing cells adjacent to Cell #1 is transmitted as the notice information.
Next, the mobile station 700 which has received the neighbor cell information performs neighbor cell search of Cells in the neighbor cell information (Step S92). Namely, the mobile station 700 measures the situation regarding wireless communication for the neighbor cells, Cell #2, Cell #3, Cell #4, Cell #5, Cell #6 and Cell #7. Further, on the basis of the measuring result, the mobile station 700 performs continuation of connection to Cell #1, handover to another cell and so forth.
Next, as another utilization example of the neighbor cell information, referring to FIG. 3, explained is a sequence at the time of executing handover which is performed by setting handover parameters from the base station 900. The sequence in FIG. 3 is handover control from a system side.
The base station 900 lets the mobile station 700 perform Measurement Configuration of the neighbor cells adjacent to Cell #1. This is, for example, for handover.
Firstly, for performing Measurement Configuration of the neighbor cells of Cell #1, MeasurementConfiguration Message is transmitted from the base station 900 to the mobile station 700 by use of RRCConnectionReconfiguration Message (Step S93).
In a case where the mobile station 700 normally accepts the RRCConnectionReconfiguration Message, the mobile station 700 transmits RRCConnectionReconfiguration Complete to the base station (Step S94). Further, in addition, the mobile station 700 begins measurement of peripheral cells of the mobile station 700. This measurement is performed on the basis of the neighbor cell information of Cell #1 included in MeasurementConfiguration Message. Namely, the measurement is performed for the neighbor cells, Cell #2, Cell #3, Cell #4, Cell #5, Cell #6 and Cell #7.
The mobile station 700 detects and measures neighbor cells existing within a condition of RRCConnectionReconfiguration and then transmits Measurement Report to the base station 900 specifying PCI (Physical Cell Identity) (Step S95). On the basis of MR (Measurement Report), the base station 900 performs handover to, for example, a cell whose reception level is large (Step S96).
Further, concrete examples of communication systems utilizing such neighbor cell information is disclosed in PTL 1 and PTL 2.
PTL1 discloses to differentiate a content of neighbor cell information according to a communication system to which a terminal conforms. This enables to prevent search of cells to which each terminal does not conform.
Also, PTL2 discloses to perform handover on the basis of neighbor cell information and to adjust handover parameters for preventing handover failure.